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(meteorobs) Leo 2001 coverage in S&T 3/2002
Am I the only one unhappy with the coverage of the 2001 Leonid storms
in the new Sky & Telescope? Here is a letter I just sent them; as it
exceeds their 300 words limit, it'll probably not make it into the
magazine in full, so here is a "preprint":
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The coverage of the Leonid meteor storms of 2001 in the March
2002 issue of Sky & Telescope seems strangely behind the times:
Hard-working meteor researchers, mainly in the amateur
community, have spent the last decades developing systematic
methods for judging the strength of meteor outbursts - and all we
get from the most influential astronomy magazine on the planet
is a bewildering collection of individual soundbites and completely
unreduced personal meteor counts. The numbers in the text as well
as the plot on p. 104 are simply useless as no correction for the
limiting star magnitude and especially for the elevation of the
radiant was made - and the latter can change the perceived
meteor rate by a factor of several.
Simply put the number of meteors you see is the full number
multiplied with the sine of the radiant's (in our case, the Lion's
head's) altitude: If it is near the zenith, there is hardly any
correction, if it is at 45 deg., you lose 30%, at 35 deg. you lose
42% and at 25 deg. 58% of all meteors. This is why calculating the
Zenithal Hourly Rate (ZHR) is not a numbers game but the one and only
way to find out what really happened. And if the observations of
enough observers are used, the result tends to be quite consistent
and the ZHR plot remarkably smooth. Within days of the 2001
Leonids storms the picture was emerging, as could be followed on
a number of meteor websites and mailing lists: The "American"
peak reached a ZHR of some 1700, the "Asian-Australian" one
peaked near 3500. Thus both 2001 storms actually fell short of
the strength of the single-peaked Leonid storm of 1999 when the ZHR
reached some 5000.
Sky & Tel's statement that "during the previous half century
only the brief Leonid outburst of 1966 exceeded the intensity of
last November's display" therefore holds only true for the
Americas and not at all for the whole word. The 1999 storm could
be seen in all its glory - and with the radiant very high in the sky -
from the Middle East: Having been a witness to the latter as well as
the larger Asian peak of 2001 (from South Korea, with a lower radiant),
I can testify that, while in 2001 the meteors were generally
brighter, the impression of a real rain of meteors from the sky
was indeed much more pronounced in 1999. And at times, in the
desert of Jordan that night, I even shared the impression which
Robert Liefeld recalls from the 1946 Giacobinid meteor storm (on
p. 103): In 1999, too, it "felt like you were looking up at a cone of
light falling from the sky."
Relevant links can be found in the sidebar of the lead story of
http://www.astro.uni-bonndot de/~dfischer/mirror/230.html and the
latest ZHR profile is at http://www.imodot net/news/l01fin_a.gif
Daniel Fischer
Koenigswinter
Germany
dfischer@astro.uni-bonndot de
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